1. Field of the Invention:
The present invention relates to a water-cooled electrode for being attached to the shank of a resistance welding machine.
2. Description of the Prior Art:
Conventional resistance welding electrodes of various types include a barrel-shaped portion leading to an electrode end portion and having a coolant passage defined therein. Since the coolant passage terminates short of the electrode end portion, the coolant flowing in the coolant passage has failed to cool the the electrode end portion sufficiently. The electrode end portion has an enlarged portion of a larger diameter. During repeated welding operations, the electrode end portion is deformed into a mushroom-like formation, which reduces the density of an electric current flowing through the electrode, thus failing to form a weld spot or nugget effectively.
One prior solution has been to form a cylindrical projection integrally with the end portion, the cylindrical projection having annular ridges and grooves thereon for reducing the mushroom-like deformation.
Such an electrode arrangement is disclosed in U.S. Pat. No. 4,476,372. As shown in FIG. 4 of the accompanying drawings, an electrode 11 has a coolant passage 12 defined therein and includes a cylindrical projection 14 extending from an end 13 and having integral annular ridges 15. The cylindrical projection 14 therefore has alternate larger and smaller diameters in the axial direction thereof. During repeated welding operations, the tip end of the cylindrical projection 14 is progressively worn and spread radially outwardly into a mushroom-like formation. Since the mushroom-like formation is cut off by the next groove, the prior electrode construction is effective in removing the mushroom-like formation. However, as the tip end of the cylindrical projection wears during repeated welding operations, it abruptly varies in diameter between the larger and smaller diameters, with the result that the density of an electric current flowing through the electrode is sharply varied alternately between high and low levels. The varying welding electric current is apt to form irregular weld spots or nuggets, with the consequence that no accurate and adequate welding operations will be carried out.